Many packaging applications, especially food packaging, require or benefit from the use of bags made from various thermoplastic materials and structures. Examples of commercial bags include heat shrinkable bags supplied by the Cryovac Division of W. R. Grace & Co.-Conn., including the L 340, B620, and B2550 bags.
These bags are commonly used in large scale meat processing and/or packaging systems where production speed and efficiency are important. Bags to be used in these systems are often themselves packed in boxes, the individual bags taped together so that they will feed in a predictable and efficient manner to an article loading station. Typical of such technology is U.S. Pat. No. 3,161,347 (Hannon), disclosing a tape to which bags are attached, and U.S. Pat. No. 3,587,843 (Wing), incorporated herein by reference in its entirety, disclosing two tapes to which are attached imbricated (i.e. shingled) bags.
At the loading station of a conventional system, each bag is opened and then loaded with an article such as a fresh red meat subprimal or smoked and processed meat, poultry, cheese, or other perishable food product, or other product.
One problem sometimes encountered is that of bag lips (the edges of the bag panels which form the bag opening) which can be undesirably stuck together, or stuck to the adhesive bag tapes. This can mean a significant slow-down in a packaging line, and down-time for the food processor or other user of bags. The bags can of course be opened manually, but this is very slow and labor intensive. It also risks unnecessary handling of the bag.
Some solutions have been offered to deal with the problem of opening a bag prior to the insertion of an article into the bag. The use of air pressure or vacuum is common, but of course requires a source of vacuum or air pressure. Sometimes the use of air pressure is unpredictable in providing consistent bag opening performance. Even in the case of air pressure, the worker sometimes needs to manually start the opening process so that the air can be effective in further opening the bag sufficiently to allow an article to be loaded therein.
It is desirable to provide a method and bag which lessen or eliminate the requirement of opening the bag manually, or of using vacuum or air pressure. It is also desirable to provide a method of opening the bag in a reliable and consistent manner, which allows for increased automation, and potentially reduces operating costs.
Another problem inherent in conventional bag loading systems is the requirement to match center to center tape spacing to the bag size and article cross section. "Tape spacing" here refers to the pair of adhesive carrier tapes, e.g. as described in the '843 Wing patent, which in many commercial bag loading systems hold bags together before loading with an article. Currently, the nature of the tape spacing will generally define the shape of the bag when it is opened. Since the bag dimensions are ideally matched to the dimensions of the article to be packaged, tape spacing is an important parameter in loading a bag with an article. It is desirable to provide a method and bag which lessen or eliminate the requirement of matching tape spacing to article size, i.e. of optimizing tape spacing for feeding or indexing the bags.
Still another problem often encountered in the packaging of food products is that the corners of each bag tend to curl over during bag advance and loading. This can sometimes complicate or slow the bag loading process. By finding a way to widen the tape spacing, that is, by placing the tapes closer to the bag's respective lateral edges, without being unduly limited in the need to match tape spacing to bag and article size, this problem is lessened or eliminated.
An additional problem is the variation in tape alignment and in spacing between successive bags in a stacked array of imbricated bags.
It is desirable to provide a method and system for accurately locating and positioning bags in an imbricated bag system.